Rotary pump for pumping gases



May 20 1924. 1,494,758

0. SEITZ ROTARY PUMP FOR PUMPING GASES Filed June 20. 1923 Fig.2.

$7 .5. K Fig.4.

[21 27 6.2L 2; or i Oslwir 561 62 j EM Patented May 20, 1924.

" 2' oFF #11::

OSKAR SEITZ, OF BADEN, SWITZERLAND, ASSIGNOR TO AKTIENGESELLSGHAFT BROWNI BOYERL AND CIR, OF BADEN, SWITZERLAND.

ROTARY PUMP FOR PUMPING GASES.

Application filed June 20, 1923. Serial No. 646,696.

To all whom it may concern:

Be it known that I, OSKAR Snrrz, a citizen of the Swiss Republic,residing at Oberer Kapperlerhof, Baden, Switzerland, have in- 8 ventedcertain new and useful Improvements in Rotary Pumps for Pumping Gases,of which .the following is a specification.

In rotary pumps with an air vessel, such as are employed for generatinghigh "acua,

1 by means of an oil return duct arranged as a by-pass around thedelivery valve, a certain quantity of oil is allowed to flow backcontinuously during the working of the pump, said oil serving as a sealbetween the 15 moving parts. When the pump is stationary theatmosphericpressure acting upon I the oil in the air vessel forces this oil backthrough the oil return duct and the leaky places between the movableparts in the interior of thepump back into the oil reservoir. Thisreturn of the oil may be prevented by means ofa closing device, .such asfor instance, a float valve located betweenthe pump and the oilreservoir. This float valve, while the pump is stationary, is caused tofloat by the returning oil, and it finally shuts off the return oftheoil by closing a passage aperture.

That manner of shutting oil the return of the oil has however thefollowing drawbacks: The oil in the air vessel usually contains numerousbubbles of air under atmospheric pressure. When the pump is stationary,these bubbles of air pass with the oil into the interior of the, pumpand into the suction passage as far as the float valve. Here they expandand penetrate into the reservoir before the float valve can close.Further, the oil in the air vessel contains moisture which is likewisecarried over and, byreason of its high vapour tension, will spoil thevacuum when the pump is started again, until all the moisture has beentransferred back to the delivery side. Moreover, impurities are carriedover by the returning oil and are liable subsequently to interfere. withthe workin of the pump. Finally the fact that the oiI does actuallypenetrate into the interior of the pump is a great drawback because thenthe pump must be started with a much greater torque than the normal. 1

In order to obviate the first mentioned drawback, namely the penetrationof air into the reservoir past the too-slowly operating closing device,instead of efiecting the closure by means of a float valve whichoperates only when the pump has already come to a standstill, and thereturn flow of the oil has begun, the said closure is effected accordingto this invention by means of a closing device which closes the returnpassage for the oil immediately when the rotational speed of the pumpdrops below a determined value. The rotational speed at which theclosing device is opened and closed, must be set so high that the pumpon attaining said speed shall ener ate a sufficient pressure to revent te oil from flowing back through t e pump. For this purpose the closingdevice may be con-. trolled for governor which is mounted eitherdirectly instance by a certrifugal upon the driving shaft of the pumpor' is coupled mechanically by means of a clutch to the said pump. Inorder to make the overall length of the pump as short as possible, thecentrifugal governor may be structurally comprised within the clutchhalf on the pump side.

A further modification is the controlling of the closing device by oilpressure generated by an oil pump mounted on the shaft of the air pump.In order to reduce the overall length of the pump. as much as possiblethe oil pump may be structurally comprised within the casing of the airpump.

Three embodiments of this invention are illustrated by way of example inthe accompanying, drawings in which Figure l is a cross section of arotary pump, of the hitherto usual construction. In the figures, is therotor of the pump; 6 is the suction duct; 0 is the .float valve closingthe suction duct; d is the dellvery duct; e is'the delivery valve; 7' isthe air vessel' the oil in which is under atmos- 'pheric ressure; and gis the oil, return duct. en the pump is stationary the oil penetratesfrom the air vessel f through the oil return duct 9, the delivery duct1!, the leaky place at the periphery of the pump rotor a and the suctionduet b up to the EEQ. V 1 1,494,758

' a height as to lift the float valve and thus prevent furtherpenetration of the ,oil.

5 Figures 2 to 4 illustrate three construc- In these tional examples ofthe invention. figures the lettersa, b, c, d, e, f, 9 have the samesignificance as in Figure 1. h is the closing device designed to prevent'the return of the oil when the pump is ,stationary. In Figures 2 and3 2' is a certrifugal governor; k is the sleeve of said governor. Thelift of said sleeve is transmitted through rodding Z to the closindevice 7).. 11 Figure 4, m is an oil pump which, when the pump isrotating, generates oil pressure in the cylinder 11 o is a piston whichis moved in said cylinder by theoil pressure so as to operate theclosing device h; p is a spring which'has a constant tendency-to movethe piston 0 in opposition to the oil pressure; 9 is apressure-equalizing duct connecting the cylinder 11 with the main oilchamber of the air pump.

Figure 2 is a longitudinal section of an ,improved rotary pump whereinthe closing device 72- is operated by a centrifugal gov- 'ernor z' andisstructurally contained in the delivery duct d between the rotor and thedelivery valve.

Figure 3 is a longitudinal section of an improved rotary pump whereinthe closing device h is structurally contained in the oil return duct g.The said return duct in this -modification has a form such that it canbe controlled directly by a piston.

Figure 4 is a longitudinal section of a portion of an improved rotarypump wherein, the closing device is controlled by oil pressure by meansof an oilpump m. In this construction the oil pump is shown as i arotary pump (gear ump). A pump of this kind has a determined deliveryvolume 7 not a determined pressure. I

ever to obtain at a desired speed of rotation for a determined speed ofrotation, but has In order howthe pressure which is just able to movethe piston o, the delivered oil in' front of the piston 0 may beallowedto flow ofi through a duct the flow-resistance of whichis suchthat thequantity of oil delivered at a de-.

a centrifugal'pump may be employed which without such devices willgenerate an oil pressure increasing with the rotational s eed. That partof the cylinder n inwhich te spring p is contained communicates by wayof a pressure-equalizing *duct q with the main oil chamber of the pump,in order that no counterressure shall be able to be produced in sai partofthe cylinder.

The operation of a pump constructed according to this invention is asfollows As will be tional examp es, when the pump is stationary, theclosing device It is in its closed position so that it is not possiblefor the oil to flow from the air vessel in which atmospheric pressureexists back into theinterior of the pump.

On starting the pump, either I the centrifugal governor '1: movesoutwards (Figs. 2 and 3), and its sleeve moves towards the clutch halfand by means of the transmission roddin 1, causes the closing device hto open the elivery duct d or the oil return duct g, or (as shown inFig. 4) the oil pump m places the cylinder n under oil pressure, andthis oil pressure moves the piston a so that the closing device itlikewise opens the oil return duct; the spring p being compressed. Ifthe rotational speed of the pump drops to such an extent that erceivedfrom all the constructhere is a risk of the oil flowing back I throughthe pump, the centrifugal goverthe air vessel is thus unable to get pastthe said closin'g device.

WhatI claim is 1. In a rotary pump comprising an air vessel for pumpinggases, an oil return duct, and a closing device for preventing the oilfrom returning from. said air vessel into the pump cylinder, throughsaidoilreturn duct, the combination of meansfor causing said closingdevice to close said oil return duct immediately the rotational speedof. l

the pump falls below a determined limit.

\ 2. In a rotary pum comprising the combination claimed in c aim 1, theadditional combination that the closing device is operated by acentrifugal governor actuated by a moving part of the pump.

3. In a rotary pump comprising the combination claimed in claim 1 andthe addi tional-combination claimed in claim 2, the further combinationthat the centrifugal governor is located in the interior of the usualclutch half on the pump side. i

4. In a rotary pum comprising the combination claimed in c aim 1, theadditional combination that the closing device is .operated by oilpressure generated by a pump coupled to the air pump.

5; In a rotary pump comprising the combination claimed in claim 1 andthe additional combination claimed in claim d, the

1,404,7ae t 3 further feature that the oil pump is 10- bi'nation claimedin claim 1, theadditional cated in the interior of the air pump casing.feature that the closing device is located in 6. In a rotary pumpcomprising the comthe oil return duct. 1 bination claimed in claim 1,the additional In testimony whereof I have signed my 5 feature that theclosing device is locatedin name to this specification.

the delivery duct.

7. In a rotary pump comprising the com- OSKAR SEITZ.

